For something that is actually interesting, a RM564
Is this something reasonable for someone (me) who has not worked on one of these before?
I like the idea that it is rack mountable... might be worth a low-ball offer.
Biggest problem is that it is far away, closer to where the dwagon lives used to live.
Here ! I was in your position 4 years ago when I embarked into the restoration of my first tube anything, a Tek 317 scope.
Here is my take on it.
1) Don't know about the Canadian market, but here a rack mount Tek scope of any model and vintage is very rare. So if really you want a rack mount Tek scope, the obvious is to get it before someone else does, especially since the price is fair as it is. If you get to start work on it in a year or two only, and have by some miracle found another rack-mount scope that you like better, you can always sell the firsts one if you want to, but more likely you will keep it as a part mule to help you fix the "new" one. Being able to to quickly swap tubes is priceless. Saves you from buying new tubes you might not even need, and waste time waiting for them being delivered.
2) As was said, if really you feel overwhelmed by that (apparent only) complexity of a Tek tube scope, yeah why not get some simpler piece of tube equipment.
3) 564 is all tubes no trannies, well according to Tekwiki at least. 564B is 100% PCB and transistors, well I mean the chassis itself only. The plug-ins of course are whatever you decide to use, so will probably be tube based.
4) Look at pics of the 564 on Tekwiki : once you remove the plugins, the circuitry of the main frame is readily accessible on both side, just pop the top and bottom covers and your right there probing around.
5) Cats and humans : doesn't your lab have a door that can close ?! If you are in the lab, well of course you are there to tell people to be careful, but I guess by now they must already know they should not approach or touch stuff plugged in on the bench anyway ?!
Then when you are NOT in the lab hence can't see what others are doing... well I will state the obvious and say that you should not leave an old tube scope unattended for too long... just in case !
If you need/want to anyway, well just close the door. IF it does not have a key... put a huge red sign on the door to INSTRUCT people not to enter because of dangerous high-voltages on the bench.
6) Learning tubes. I don't know how little you know. You probably know more than I did. I am not that old so never learned anything about tubes at school. Didn't even know they existed. So to me they couldn't possibly be more mysterious... I had no idea what principles governed their operation, had n idea what all the pins did, had n idea what all the weird looking symbols meant on the schematics. It was black magic to me, pure and simple. Alien.
So I too was scared and reluctant at first, fearing for my safety and feeling I would be too incompetent to fix it. But you know what ? It's all BS ! As Mansaxel said, tubes are very simple ! Of course you can come across the odd one with a weird failure mode... but you get to know the various failure modes, just like any device, no big deal. Plus in practice most of them aren't defective.. they are just "tired", low gain, that's all.
It's not like solid-state was any better ! They too can have their weird failure modes too ! An intermittent bond inside an IC package isn't exactly the most obvious and fun thing to debug for a new comer I would think !
Plus, you don't even need to be an expert in all faluure modes (certainly I am NOT !
) to be able to tell if a tube is bad !
In practice what you do is work on a particular section of the circuit, say stage 3 of the vertical amplifier or whatever... you see the signal coming in is good, coming out isn't good any more, so you know something is going on there. Can be either the tube or the discrete components around it. So you just check supply voltages, then look for visual clues of a damaged discrete component, then measure them quickly with your DMM.. if all is well then just swap the tube as see if that fixes it ! Job done. Next.
The good thing with old Tube Tek scopes is they all have a very comprehensive service manual. Block diagram, and a lengthy description of how each and every section of the scope works. The on the schematics, you have test points showing DC voltages as well as waveform.
So you just go through that calmly, methodically... and you will fix that scope I am sure ! Plus of course, you are not alone ! You can post on here, and of course subscribe to the "Tekscope" mailing list, where all the tube Tek grey beards/experts reside ! They have alwyas been very friendly and helpful to me !
To make sense of the schematics : it's easy, no really ! Just consider the tube as FET transistor...3 pins. The "grid" is like the gate, "anode" is like the drain, and the "source" is like the cathode. That's all. You give the anode some juice, 200 or 300 or 500 volts, apply some voltage at the grid and you will get more or less current flowing between the anode and cathode. That's it basically ! Don't care about all the other pins ! You have two pins for the filament/heater... all you need to know is that it's powered on all the time and is required for the tube to work. It's merely an accessory. You need it, you know it's there, but it's not required to understand/read the schematics. So much so that as you will see, the filaments are not even represented in the schematics ! You only see them appearing once, all grouped together, in the power supply schematic.. of course, because you need to power these filaments. But in all other schematics, every time you se a tube symbol, you will NOT see the filament. It's just not required to the understanding of the circuit.
What you might see in schematics is EXTRA pins here and there.... A "Triode" as its name suggests, as only 3 active pins : the 3 pins analogous of the FET transistor discussed above. It's the bare minimum you need for the thing to work. but you can also have a "Pentode" tube.. again as the name suggests, it has 5 pins not 3. However, these two extra pins... you don't even need to care about 99,999999% of the time. The designers had to care... but for repair purpose, just ignore them plain and simple. Usually tehy are just tied to fixed potential via a high impedance resistor divider, and often times, these extra pins are simply tied directly to one of the other power supplies, or to the cathode.... really you can just ignore them. Just look at the grid/anode/cathode, that's, the "transistor".. it's all that you need to understand how things work. Sometimes, one of these two extra pins will NOT even be accessible ! It will already have been, internally, connected to the cathode or whatever.
Once you have all that in mind... you can read the schematic easily. Every time you see a tube you just see a FET transistor, and then suddenly it all seems simple and clear as water !
.... and you will realize that all the common transistor circuits you learned at school, astable/multivibrator, flip-flop, amplifiers, voltage regulators etc... were not transistors inventions... they were already all designed and working with tubes, and only adapted later to make use of trannies.. just adapted, not invented, not new stuff... there is no black magic at all in tube circuits !
So... I say, grab this rack mount scope while you can because god knows how long it might be before you can find another one especially at a fair price like this. Then you have all the time in the world to see how you want to proceed about it...
Pop the covers, see for yourself how it's put together. Read the manual, identify where each section is.. familiarize yourself with the scope...
If you still don't feel like going straight at it, yeah as was suggested, why not grab whatever cheap piece of junk TE that's got tubes in it but is simpler in design, less tubes.. and get some hand-on experience on it.. then start probing around your Tek scope progressively, a step at a time !
Have fun, I sure do !!!